Hello. Does your SG-250 also has such small " nick" on top surface ? When I got it brand new, there was a light spot on grindstone, after first trueing I noticed a very small hole, I thought, that it will go away, but now my grinding stone has a diameter about 243 and the hole gets bigger. Is it normal or I have a faulty grindstone ? I'll listen any suggestion 
I'll include a link with pictures http://nagi.ee/photos/tartustuff/sets/404891/
I'll include a link with pictures http://nagi.ee/photos/tartustuff/sets/404891/